Electronic devices are commonly used in varied applications. In the particular case of power electronic devices, they are constructed so as to be able to withstand a relatively high operating power (for example, of the order of 100-625 W).
Power electronic devices include electronic power components (such as power transistors and power diodes) which are typically integrated in chips made of semiconductor material. Each chip is then placed in a suitable package, which protects the chip at the same time allowing access to its terminals. The package comprises an insulating body that incorporates the chip. The insulating body exposes various leads, each of which is electrically connected to a corresponding terminal of the chip; typically, the lead is connected to the terminal of the chip with a wire connection technique (wire-bonding), in which a conductive wire is fixed at one end thereof to the lead, and at another end thereof to the terminal of the chip. The leads of the package are used to connect the same (and hence the corresponding terminals of the chip) to external circuits. For this purpose, the electronic device is typically mounted on a Printed Circuit Board (PCB). For example, in Surface Mount Technology (SMT) the leads are temporarily attached, by means of solder pastes, to corresponding conductive tracks of the printed circuit board by means of a slight pressure (pick and place), and are then welded on the same by reflowing.
Power electronic devices are subject to considerable heating during their operation (as they are affected by high currents and/or voltages, of the order of 50-1500V and 0.1-8A, respectively). Therefore, the package of each electronic power device is typically equipped with a heat sink, which presents a large exposed surface on a mounting surface of the insulating body on the printed circuit board; the chip is fixed on the heat sink, so as to facilitate the transfer of heat produced by the same outside of the package (so as to reduce the thermal resistance of the electronic device from its chip to the external environment). The heat sink can also be electrically connected to a terminal of the electronic device integrated in the wafer, so as to act also by the corresponding lead—for example, when the electronic device has a vertical structure with such a terminal formed on a rear surface of the chip that is fixed on the heat sink (while the other terminals of the chip, implemented on a front surface thereof, are connected to the respective leads via conductive wires).
A typical application of power electronic devices is in protection circuits for battery packs. A battery pack includes a plurality of batteries connected between a positive terminal and a negative terminal. In order to protect the battery pack and control the voltages which are established between the positive and negative terminals of the battery pack and the currents that flow to/from these terminals when the battery pack is connected to a load or to a generator, instead of directly connecting the load/generator to the terminals of the battery pack, it is connected to an input/output port coupled to the terminals of the battery pack through a suitable protection circuit. A generic protection circuit for battery groups (from now on simply “protection circuit”), comprises a pair of electronic power switches (for example, power transistors of the MOS type). The power transistors are arranged in series between a terminal of the battery group (for example the positive terminal) and a terminal of the input/output port. Suitably driving control terminals of the power transistors, it is possible to adjust the flow of current to/from the battery pack during charging phases (when the battery pack is connected to a generator) or discharging phases (when the battery pack is connected to a load), and, when necessary, to inhibit the passage of current by electrically insulating the terminals of the battery pack from the input/output port. The two main types of protection circuit provide that the power transistors are NMOS transistors of power connected in common-drain configuration, or that they are power PMOS transistors connected in a common source configuration.
The power transistors are typically integrated into distinct chips (for reasons both technical and economic), which chips are then housed in corresponding packages. Therefore, the protection circuit includes a separate package for each power transistor, which is mounted separately on the printed circuit board (which implements the desired electrical connection between the various power transistors).
These solutions are not however completely satisfactory—for example, as regards their dimensions, their constructive complexity, and their heat dissipation efficiency.
There are additional solutions that provide for a single package for housing two power transistors connected in series. However, currently such solutions are suitable only to pairs formed by power NMOS transistors connected in a common drain configuration, and to pairs formed by an NMOS transistor and a PMOS transistor connected in a common drain configuration.